DISKLABEL32(5) BSD File Formats Manual DISKLABEL32(5)NAMEdisklabel32 — 32 bit disk pack label
SYNOPSIS
#include <sys/disklabel.h>
DESCRIPTION
Each disk or disk pack on a system may contain a disk label which pro‐
vides detailed information about the geometry of the disk and the parti‐
tions into which the disk is divided. It should be initialized when the
disk is formatted, and may be changed later with the disklabel32(8) pro‐
gram. This information is used by the system disk driver and by the
bootstrap program to determine how to program the drive and where to find
the file systems on the disk partitions. Additional information is used
by the file system in order to use the disk most efficiently and to
locate important file system information. The description of each parti‐
tion contains an identifier for the partition type (standard file system,
swap area, etc.). The file system updates the in-core copy of the label
if it contains incomplete information about the file system.
The label is located in sector number LABELSECTOR of the drive, usually
sector 0 where it may be found without any information about the disk
geometry. It is at an offset LABELOFFSET from the beginning of the sec‐
tor, to allow room for the initial bootstrap. The disk sector containing
the label is normally made read-only so that it is not accidentally over‐
written by pack-to-pack copies or swap operations; the DIOCWLABEL
ioctl(2), which is done as needed by the disklabel32(8) program.
A copy of the in-core label for a disk can be obtained with the
DIOCGDINFO ioctl(2); this works with a file descriptor for a block or
character (``raw'') device for any partition of the disk. The in-core
copy of the label is set by the DIOCSDINFO ioctl(2). The offset of a
partition cannot generally be changed while it is open, nor can it be
made smaller while it is open. One exception is that any change is
allowed if no label was found on the disk, and the driver was able to
construct only a skeletal label without partition information. Finally,
the DIOCWDINFO ioctl(2) operation sets the in-core label and then updates
the on-disk label; there must be an existing label on the disk for this
operation to succeed. Thus, the initial label for a disk or disk pack
must be installed by writing to the raw disk. All of these operations
are normally done using disklabel32(8).
The format of the disk label is specified in <sys/disklabel32.h>.
SEE ALSOdisklabel64(5), disktab(5), disklabel32(8)BSD August 21, 2008 BSD
